1. Field of the Invention
The present invention relates to a method and a device for upgrading a guest Operating System (OS) of an active Virtual Machine (VM).
2. Description of the Related Art
Availability is a key factor for evaluating system performance. The availability means a degree to which a system, a sub-system, or a device providing services is operable and in a committable state at the beginning of a task, when the task is called at an unknown or random time. Briefly speaking, the availability can be represented by a proportion of time in which a system is in a functioning condition. In order to achieve high-availability (HA), a number of techniques have been developed in many aspects, such as hardware-level HA devices, software-level HA middleware, clusters, HA-oriented application programming model, and so on.
Currently, a technical trend of IT systems is service-oriented architecture (SOA), a basic concept of which is to set up many isolated, reusable, and independent services which can be integrated easily. Virtualization becomes a good platform to host a number of such independent services; in particular, multiple VMs that are independent of each other are set up on a physical machine, and each of the small services runs in the respective VMs. Thus, the virtualization is capable of incorporating a number of independent VMs providing various services into a physical server, such that the customer's cost for owning such a system capable of providing the various services is reduced, the whole system is easy to be managed, and resources of the physical server can be utilized more efficiently. Therefore, the need for over-provisioning resources for a single workload spike is removed.
However, one problem with a conventional IT system using a VM is how to update a platform supporting a provided service, for example, an OS of the VM in which the service resides (i.e. a guest OS), while keeping the availability of the service. Generally, after a patch for upgrading the guest OS is installed into the guest OS of the running VM (i.e., the active VM), the VM often needs to be rebooted, which renders the service provided by the VM unavailable during the rebooting.
In consideration of the above problems, the present invention provides a method and a device capable of upgrading a guest OS of an active VM while keeping availability of a service.